Lightly toast the bagel halves and place them on a serving plate.
Arrange the sardines over one half of the bagel.
Heat a little olive oil in a frying pan and cook the asparagus over medium heat.
Halve the cherry tomatoes and add them to the pan once the asparagus has started to soften.
Add the balsamic vinegar and cook for another couple of minutes until the tomatoes are slightly softened and glossy.If using, add the garlic and a pinch of chilli flakes for extra flavour.
Spoon the asparagus onto the other half of the bagel and divide the tomatoes between both halves.
In the same pan, cook the egg to your liking.
While the egg cooks, arrange the avocado slices over the sardines and drizzle with a little lemon juice to stop them browning.
Place the cooked egg on top of the asparagus half.
Scatter with chopped parsley and serve immediately.